A micro-Fenton coupled electrochemical iron removal method

Abstract

This invention discloses a micro-Fenton coupled electrochemical iron removal method. The method includes the following steps: 1) adjusting the pH of source well water or injection water used for oilfield extraction; 2) passing the pH-adjusted source well water or injection water into an iron removal device at a certain flow rate. The iron removal device is filled with spherical packing material between the anode and cathode, and a micro-Fenton coupled electrochemical catalytic oxidation reaction is carried out under direct current conditions to remove Fe. 2+ Oxidized to Fe 3+ The other part of Fe 2+ The ions react with the hydration layer on the surface of the filler and are oxidized to Fe. 3+ This oxidizes all ferrous ions; 3) The water treated by the iron removal device described in step 2) enters the coagulation and clarification tank, causing Fe... 3+ The iron is removed by forming Fe(OH)3 precipitate, thus completing the iron removal process for source water or injection water used in oilfield extraction. This invention adds an induced electric field-catalytic packing material to conventional electrochemistry, enabling rapid and efficient oxidation of divalent iron in water, and achieving iron ion removal through coagulation.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater treatment and relates to a micro-Fenton coupled electrochemical iron removal method. Background Technology

[0002] Water injection is a commonly used secondary oil recovery technology in oilfield development. Different polymer systems are typically used in the water injection process, and the compatibility between the injected water and the polymer is a key factor affecting the success of the injection. In actual water injection processes, it was found that Fe... 2+ and Fe 3+ The content of iron often has an adverse effect on the viscosity of the polymerization system. Therefore, the total iron content of the water used for polymerization or the water used for injection is generally required to be no more than 0.5 mg / L.

[0003] The current methods for iron removal are as follows: (1) Chemical oxidation method, which mainly includes natural oxidation method, contact catalytic oxidation method, and chemical agent oxidation method. Natural oxidation method consists of an aeration tank and a sedimentation tank / filter. In the aeration tank, the divalent iron in the water is oxidized to trivalent iron by aeration and oxygenation. The trivalent iron is precipitated from the water in the form of hydroxide, and then removed from the water by precipitation or filtration, thereby achieving the purpose of iron removal. This reaction needs to be carried out under the condition that the pH value of the treated water is greater than 7.0, and the reaction time is about 1 to 3 hours. At the same time, due to the high dissolved oxygen content in the effluent, the risk of corrosion of equipment and pipelines will increase. Therefore, it is not suitable for the treatment of high-salt and high-temperature injection water. Contact oxidation iron removal is to rapidly oxidize divalent iron to trivalent hydroxide under the action of filter media with catalytic effect, and trap it in the filter layer, thereby removing it from the water. The oxidation reaction mainly occurs on the catalytic oxidation film attached to the surface of the filter media. It takes about a week to form a mature catalytic oxidation film. Before the film is successfully attached, the iron removal efficiency is low. Chlorination oxidation and potassium permanganate oxidation methods utilize the oxidizing properties of chemical substances to oxidize ferrous iron to ferric iron, which is then removed as a precipitate in the form of hydroxides. Due to the extremely high salt content of the injection water, there are many components that affect the reaction process, and the dosage is much greater than the theoretical calculation. The above-mentioned existing technologies are mainly applied to the iron removal process of shallow groundwater, and have problems such as long reaction time, high dissolved oxygen content in the effluent, and low iron removal efficiency, which cannot meet the process requirements of iron removal treatment of injection water with high temperature and high salinity. (2) The existing electrochemical catalytic oxidation technology applies a high voltage electric field to the electrode plate, and through the anodic reaction of the electrode plate, an intermediate product with strong oxidizing effect is first generated, and then the generated active oxidation product oxidizes the pollutants to achieve the purpose of degradation. The existing electrochemical catalytic oxidation has the following disadvantages: 1) The existing electrochemical catalytic oxidation electrodes mostly use DSA electrodes. The substrate of this electrode is easily oxidized at high potentials, but if a sufficient amount of oxidizing active substances are to be generated in the treated water between the electrodes, a high potential is required, and the applied voltage is about 6V or more, so the electrode life is affected. 2) Due to the high potential difference of the electrodes, some ions accumulate on the electrodes, forming a concentration polarization layer, which hinders electron transfer and reduces oxidation efficiency. 3) Due to the high applied voltage, the existing electrochemical catalytic oxidation process will cause an oxygen evolution reaction at the anode, generating oxygen and increasing the dissolved oxygen content in the treated water, thereby exacerbating the corrosiveness of the treated water. Summary of the Invention

[0004] The purpose of this invention is to provide a micro-Fenton coupled electrochemical iron removal method.

[0005] The micro-Fenton coupled electrochemical iron removal method used in this invention differs from the aforementioned iron removal methods in its oxidation mechanism. The micro-Fenton coupled electrochemical iron removal method used in this invention adds an induced electric field-catalytic packing material to the conventional electrochemical technology. Under the action of the applied electric field, the packing material is polarized to form numerous charged microelectrodes. At the same time, a large number of oxide groups are formed in the hydration layer around the packing material, thereby rapidly and efficiently oxidizing divalent iron in the water and achieving complete precipitation and removal of iron ions through coagulation.

[0006] This invention provides a micro-Fenton coupled electrochemical iron removal method, comprising the following steps:

[0007] 1) Adjust the pH of the source well water or injection water used for oilfield extraction;

[0008] 2) The source well water or injection water, after pH adjustment in step 1), is passed into the iron removal device at a certain flow rate. Spherical packing material is filled between the anode and cathode of the iron removal device. Under direct current conditions, a uniformly distributed micro-electric field is induced, and numerous titanium-based graphene microelectrodes are formed on the surface coating, thereby exciting a high-density current and initiating a micro-Fenton coupled electrochemical catalytic oxidation reaction. As the water flows through the packing material, micro-eddies are formed, increasing the contact with the packing material and its hydration layer. Iron ions in the water undergo direct electron transfer with the uniformly distributed microelectrodes in the coating, thus removing Fe... 2+ Oxidized to Fe 3+ The other part of Fe 2+ The ions react with the hydration layer on the surface of the filler and are oxidized to Fe. 3+ This oxidizes all the ferrous ions;

[0009] 3) The water treated by the iron removal device described in step 2) enters the coagulation and clarification tank, so that Fe... 3+ The iron is removed by forming Fe(OH)3 precipitate, thus completing the iron removal process for the source water or injection water used in oilfield extraction.

[0010] In the above method, in step 1), the pH is adjusted to 4-5.

[0011] In the above method, in step 2), the anode substrate of the iron removal device is made of titanium material, and the coating is antimony oxide or ruthenium oxide; the cathode is made of pure titanium electrode or graphite electrode, and the limiting voltage applied between the electrodes of the anode and cathode is 0.3 to 3V, which can be adaptively adjusted according to the wastewater quality, and the electrode spacing can be 50 to 300 mm.

[0012] The reaction time can be 10 to 60 seconds;

[0013] The flow velocity can be 0.03–0.1 m / s;

[0014] The uniformly distributed micro-electric field current density can be 200–400 A / m.2 .

[0015] In this invention, the spherical filler between the plates of the iron removal device induces a uniformly distributed micro-electric field under the applied electric field, and forms numerous titanium-based graphene microelectrodes on the electrode surface coating, thereby exciting a high density of current. At the same time, the titanium dioxide component in the coating acts as a catalyst, causing the hydrated layer on the filler surface to oxidize and form strong oxidizing substances such as hydroxyl radicals and active chlorine.

[0016] In this invention, when the source well water or injection water, after pH adjustment in step 1), is injected, the water flow forms micro-vortices as it passes through the spherical packing material, increasing the contact with the spherical packing material and its hydration layer. Iron ions in the water undergo direct electron transfer with the uniformly distributed microelectrodes in the coating, thus transferring Fe... 2+ Oxidized to Fe 3+ The other part of Fe 2+ Ions react with the hydration layer on the filler surface and are oxidized to Fe. 3+ This oxidizes all the ferrous ions.

[0017] In the above method, in step 2), the spherical filler is a conductive porous filler to increase the surface area of ​​the contact surface;

[0018] The diameter of the spherical packing can be 4 to 8 mm.

[0019] In the above method, in step 2), the spherical filler is made of graphene powder, titanium oxide powder, clay and water, wherein the volume ratio of graphene powder can be 10-25%, the volume ratio of titanium oxide powder can be 6-15%, the volume ratio of clay is 60-75%, and the remainder is water.

[0020] In the above method, in step 3), at least one of alkali, coagulant, and coagulant aid is added to the coagulation clarifier to make Fe... 3+ Fe(OH)3 is formed.

[0021] In this invention, both the coagulant and the coagulant aid are conventional water treatment agents. Specifically, the coagulant is PAC and the coagulant aid is PAM.

[0022] In the above method, the pH value can be adjusted to 7-9 by adding alkali;

[0023] The dosage of the coagulant is 80-200 mg / L, and its dosage is related to the mineralization and salt composition in the water.

[0024] Settling time: 5–15 min.

[0025] The micro-Fenton coupled electrochemical iron removal process of the present invention can directly treat high-temperature and high-salinity well water and oilfield injection water.

[0026] The present invention has the following beneficial effects:

[0027] 1) Rapid oxidation of ferrous ions in the injection water: The ferrous content in the source water is 10-200 mg / L, the total iron content is 10-210 mg / L, the ferrous content in the effluent is 0-0.1 mg / L, and the total iron content is ≤0.3 mg / L;

[0028] 2) No oxidant is added during the reaction process;

[0029] 3) No oxygen evolution reaction occurs, the dissolved oxygen does not change during the reaction process, and it will not cause electrochemical corrosion of pipelines, equipment and formations by the injection water;

[0030] 4) Due to the low applied voltage, the main oxidation reaction media are the induced electric field of the internal packing and the hydration layer of the packing. Electrode oxidation and Fenton-like reactions occur uniformly in the treated water, resulting in high oxidation efficiency. Furthermore, no concentration polarization occurs at the electrodes during the reaction process.

[0031] 4) The iron removal reaction process synergistically sterilizes and removes SRB bacteria from the water, reducing the risk of microbial corrosion;

[0032] 5) It demulsifies and breaks down trace amounts of oil in the incoming water, resulting in a synergistic oil removal effect. Attached Figure Description

[0033] Figure 1 This is a flowchart of the apparatus system used in the micro-Fenton coupled electrochemical iron removal method of the present invention.

[0034] The markings in the diagram are as follows:

[0035] 1. Inlet pump; 2. Acid and alkali dosing device; 3. Iron removal device; 3.1 Electrochemical anode; 3.2 Electrochemical cathode; 3.3 Spherical packing; 4. DC power supply; 5. Clarification tank; 6. Dosing device. Detailed Implementation

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0037] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0038] This application provides a micro-Fenton coupled electrochemical iron removal method, comprising the following steps:

[0039] 1) Adjust the pH of the source well water or the water to be supplied to 4-5 by adding acid / alkali;

[0040] 2) The source well water or injection water is introduced into the iron removal system at a certain flow rate through the inlet pump to carry out the oxidation reaction;

[0041] A low-voltage direct current is supplied to the iron removal system to form an electric field between the plates; the anode substrate of the iron removal device is made of titanium material, and the coating is antimony oxide or ruthenium oxide; the cathode is made of pure titanium electrode or traditional graphite electrode, and a limiting voltage of 0.3 to 3V is applied between the plates, with a plate spacing of 50-300 mm.

[0042] The spherical filler between the plates induces a uniform micro-electric field under the applied electric field, and forms countless titanium-based graphene microelectrodes on the surface coating, thereby exciting a high density of current. At the same time, the titanium dioxide component in the coating acts as a catalyst, causing the hydrated layer on the filler surface to oxidize and form strong oxidizing substances such as hydroxyl radicals and active chlorine.

[0043] The spherical filler is a conductive porous filler with a diameter of 4-8 mm. It is made of materials such as graphene powder, titanium oxide powder, clay and water, wherein the volume ratio of graphene powder is 10-25% and the volume ratio of titanium oxide powder is 6-15%.

[0044] The uniformly distributed micro-electric field current density is 200–400 A / m²;

[0045] 3) When water flows through the packing material, it forms micro-eddies, increasing the contact with the packing material and its hydration layer. Iron ions in the water undergo direct electron transfer with the uniformly distributed microelectrodes in the coating, thus transferring Fe... 2+ Oxidized to Fe 3+ The other part of Fe 2+ Ions react with the hydration layer on the filler surface and are oxidized to Fe. 3+ This process oxidizes all ferrous ions. The reaction time is 10-60 seconds.

[0046] S60: The effluent from the iron removal system enters the coagulation and clarification tank, where alkali, coagulants, and flocculants are added to remove Fe. 3+ Fe(OH)3 precipitate is formed and removed by bottom sludge discharge.

[0047] The addition of alkali adjusts the pH value to 7-9, the coagulant dosage is 80-200 mg / L, and the sedimentation time is 5-15 min.

[0048] Example 1

[0049] like Figure 1The diagram shows a device system for a micro-Fenton coupled electrochemical iron removal method according to the present invention, comprising: an inlet pump 1 for pumping incoming water into the iron removal device at a set flow rate; an acid-base dosing device 2 for adjusting the pH value of the incoming water to 4-5; an iron removal device 3, which is a micro-Fenton coupled electrochemical oxidation generation system; wherein, an electrochemical anode 3.1, an electrochemical cathode 3.2, and a spherical packing 3.3 are filled between the plates of the electrochemical anode 3.1 and the electrochemical cathode 3.2, serving as the main site for generating the induced electric field and activating the hydrated layer; a DC power supply 4 for applying a low-voltage DC electric field to the iron removal device 3, connected to the electrodes via a power line; a clarification tank 5, where the effluent from the iron removal device 3 is mixed with liquid alkali and coagulant to form a precipitate, which is then clarified and removed; and a dosing device 6 for adding coagulant to the effluent from the iron removal device 3.

[0050] pass Figure 1 The device system shown performs a micro-Fenton coupled electrochemical iron removal method, specifically including the following steps:

[0051] The water used for water injection in an oilfield in Qinghai contains a large amount of ferric and ferrous ions. Direct injection will produce insoluble precipitates, affecting the injection effect. The physicochemical data of the initial water quality are shown in Table 1.

[0052] Table 1

[0053] project Ferrous content (mg / L) Total iron content (mg / L) Suspended matter mg / L raw water quality 53.83 60.48 156.83

[0054] The iron removal method using the packing coupling electrochemical method described in this invention employs a titanium-based antimony oxide coated electrode as the anode and a graphite electrode as the cathode. The electrode spacing is 150 mm, and spherical packing with a particle size of 6 mm is filled between the electrodes.

[0055] The pH of the water used for preparation was adjusted to 4.6, and the iron removal system was introduced. An applied voltage of 3V was set, and the induced voltage of the packing material was measured to be approximately 1.5V, with an induced current density of 380A / m³. 2 The reaction time was 50 seconds. Aluminum salt inorganic polymeric coagulant was added to the effluent at a dosage of 120 mg / L, and the sedimentation time was 6 minutes.

[0056] After treatment by the method described in this invention, the ferrous iron content decreased from 53.83 mg / L to 0.06 mg / L, with a removal rate of 99.9%; the total iron content decreased to 0.25 mg / L, with a removal rate of 99.6%; and the suspended solids concentration decreased to 6.34 mg / L, with a removal rate of 95.9%. This meets the total iron content requirements for water used in water preparation. The effluent water quality analysis is shown in Table 2.

[0057] Table 2

[0058] project Ferrous content (mg / L) Total iron content (mg / L) Suspended matter mg / L Water output results 0.06 0.25 6.43 Removal rate 99.9％ 99.6％ 95.9％

[0059] Example 2

[0060] The micro-Fenton coupled electrochemical iron removal method according to the device system in Example 1 specifically includes the following steps:

[0061] The water in the source well of an oilfield in the Bohai Sea contains a certain amount of ferrous ions, which affects the quality of the injected water and the properties of the polymer solution. The initial water quality is shown in Table 3.

[0062] Table 3

[0063] project Ferrous content (mg / L) Total iron content (mg / L) Suspended matter mg / L Raw water results 5.66 13.48 46.72

[0064] The iron removal method using the packing-coupled electrochemical method described in this invention employs titanium-based ruthenium oxide coated electrodes for both the anode and cathode. The electrode spacing is 50 mm, and spherical packing with a particle size of 4 mm is filled between the electrodes.

[0065] Water from the source well was passed into the iron removal device, and a voltage of 2V was applied. The induced voltage of the packing was measured to be approximately 0.8V, the induced current density was 200A / m², and the reaction time was 15 seconds. Aluminum salt inorganic polymeric coagulant was added to the effluent at a dosage of 180mg / L, and the sedimentation time was 15 minutes.

[0066] After treatment by the method described in this invention, the ferrous iron content decreased from 5.66 mg / L to 0.03 mg / L, with a removal rate of 99.5%; the total iron content decreased to 0.17 mg / L, with a removal rate of 98.7%; and the suspended solids concentration decreased to 7.30 mg / L, with a removal rate of 84.4%. The effluent meets the iron content requirements for injection water. The effluent water quality analysis is shown in Table 4.

[0067] Table 4

[0068] project Ferrous content (mg / L) Total iron content (mg / L) Suspended matter mg / L Water output results 0.03 0.17 7.30 Removal rate 99.5％ 98.7％ 84.4％

[0069] Example 3

[0070] The micro-Fenton coupled electrochemical iron removal method according to the device system in Example 1 specifically includes the following steps:

[0071] The water used for polymer synthesis and injection in a certain oilfield in Xinjiang has high levels of ferrous and total iron, which cannot meet the requirements for polymer synthesis and water injection. The initial water quality is shown in Table 5.

[0072] Table 5

[0073] project Ferrous content (mg / L) Total iron content (mg / L) Suspended matter mg / L Raw water results 88.64 98.27 276.56

[0074] The iron removal method using the packing coupling electrochemical method described in this invention employs a titanium-based ruthenium oxide coated electrode as the anode and a graphite electrode as the cathode. The electrode spacing is 300 mm, and spherical packing with a particle size of 6 mm is filled between the electrodes.

[0075] The water to be prepared was passed through the iron removal device. An applied voltage of 3V was set, and the induced voltage of the packing material was measured to be approximately 1.0V, the current density to be 300A / m², and the reaction time to be 30 seconds. Aluminum salt inorganic polymeric coagulant was added to the effluent at a dosage of 90mg / L, and the sedimentation time was 10min.

[0076] After treatment by the method described in this invention, the ferrous iron content decreased to 0.15 mg / L (removal rate of 99.8%), the total iron content decreased to 0.38 mg / L (removal rate of 99.6%), and the suspended solids concentration decreased to 8.35 mg / L (removal rate of 97.0%). The total iron content of the effluent meets the requirements for polyacrylamide production and water injection. The effluent water quality analysis is shown in Table 6.

[0077] Table 6

[0078] project Ferrous content (mg / L) Total iron content (mg / L) Suspended matter mg / L Water output results 0.15 0.38 8.35 Removal rate 99.8％ 99.6％ 97.0％

Claims

1. A micro-Fenton coupled electrochemical iron removal method, comprising the following steps: 1) Adjust the pH of the source well water or injection water used for oilfield extraction; 2) The source well water or injection water, after pH adjustment in step 1), is fed into the iron removal device at a certain flow rate. Spherical packing material is filled between the anode and cathode of the iron removal device. Under direct current conditions, a uniformly distributed micro-electric field is induced, forming numerous titanium-based graphene microelectrodes, thereby exciting a high-density current to carry out a micro-Fenton coupled electrochemical catalytic oxidation reaction. As the water flows through the packing material, micro-eddies are formed, increasing the contact with the packing material and its hydration layer. Iron ions in the water undergo direct electron transfer with the uniformly distributed microelectrodes in the coating, thus removing Fe... 2+ Oxidized to Fe 3+ The other part of Fe 2+ The ions react with the hydration layer on the surface of the filler and are oxidized to Fe. 3+ This oxidizes all the ferrous ions; The anode substrate of the iron removal device is made of titanium, and the coating is antimony oxide or ruthenium oxide; the cathode is a pure titanium electrode or a graphite electrode. The spherical filler is made of graphene powder, titanium oxide powder, clay and water; 3) The water treated by the iron removal device described in step 2) enters the coagulation and clarification tank, causing the Fe... 3+ The iron is removed by forming Fe(OH)3 precipitate, thus completing the iron removal process for the source water or injection water used in oilfield extraction.

2. The method according to claim 1, characterized in that, In step 1), the pH is adjusted to 4-5.

3. The method according to claim 1 or 2, characterized in that, In step 2), a voltage of 0.3~3V is applied between the plates of the anode and cathode, and the distance between the plates is 50~300mm; The reaction time is 10-60 seconds; The flow rate is 0.03~0.1m / s.

4. The method according to claim 1 or 2, characterized in that, In step 2), the spherical packing is a conductive porous packing; The diameter of the spherical packing is 4~8mm.

5. The method according to claim 1 or 2, characterized in that, In step 2), the spherical filler contains graphene powder with a volume ratio of 10-25%, titanium oxide powder with a volume ratio of 6-15%, clay with a volume ratio of 60-75%, and the remainder is water.

6. The method according to claim 1 or 2, characterized in that, In step 3), at least one of alkali, coagulant, and coagulant aid is added to the coagulation clarifier to make Fe... 3+ Fe(OH)3 is formed.

7. The method according to claim 6, characterized in that, The addition of alkali will adjust the pH value to 7-9; The dosage of the coagulant is 80~200 mg / L; Settling time: 5-15 minutes.

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